Influence of Ba/Ti Ratio on the Positive Temperature Coefficient of Resistivity Characteristics of Ca‐Doped Semiconducting BaTiO₃ Fired in Reducing Atmosphere and Reoxidized in Air

Abstract

The positive temperature coefficient of resistivity (PTCR) characteristics of donor-doped BaTiO 3 fired in a reducing atmosphere and reoxidized in air are investigated. The result reveals that conventional semiconducting BaTiO 3 ceramics fired in a reducing atmosphere and reoxidized at a low temperature of 8001C in air show minimal PTCR characteristics, as reported earlier; however, Ca-doped BaTiO 3 with compositions in the range of 1.005r(Ba1Ca1La)/Tir1.010 exhibit pronounced PTCR characteristics, even when reoxidized at such a low temperature. The semiconducting BaTiO 3 ceramics with {(Ba1 Ca1La)/Ti} 5 1.005 and Ca-doped to 20 mol% exhibit remarkable PTCR characteristics with a resistivity jump of two orders of magnitude when they have been reoxidized at 8001C after firing in a reducing atmosphere.C. Randall-contributing editor

Effects of BNT Addition on the Microstructure and PTC Properties of La-Doped BaTiO3-Based PTCR Ceramics

“…The samples sintered in N 2 had to be reoxidized in air to enhance the PTCR characteristics because of firing in reducing atmosphere the PTCR characteristics would be weakened [5,6]. The reoxidation treatment was carried out at 900-1000 • C for 1 h [7]. The In-Ga paste was applied to both surfaces of the sintered samples as the electrode, and the resistivity-temperature dependence was determined by direct measurement of current flowing through under the electric field of 0.1∼10 V/mm from room temperature to 300 • C at a heating ratio of 2 • C/min.…”

Reoxidation Effects of Ba‐Excessive Barium Titanate Ceramics for Laminated Positive Temperature Coefficient Thermistors

“…Niimi et al . proved that BaTiO 3 ceramics with excessive Ba element had a more significant PTC effect than those rich in Ti element . It was also found out that several kinds of reduced BaTiO 3 ceramics have PTCR effects but the Y‐doped sample reveal no resistivity jump at all .…”

“…Niimi et al proved that BaTiO 3 ceramics with excessive Ba element had a more significant PTC effect than those rich in Ti element. 9 It was also found out that several kinds of reduced BaTiO 3 ceramics have PTCR effects but the Y-doped sample reveal no resistivity jump at all. 10 The behavior of oxygen had been traced on reoxidized PTC ceramics, showing that the scale of the PTCR jump depends on the amount of the oxygen penetrated into grain boundary region.…”

Abnormal reoxidation effects in Ba‐excess La‐doped BaTiO3 ceramics prepared by the reduction‐reoxidation method

“…Ba‐excess BaTiO 3 ceramics was frequently used because it showed higher PTCR jump than Ti‐excess one . Generally, PTCR ceramics fired in a protective or reducing atmosphere showed poor PTCR effect, which could be enhanced through reoxidation .…”